This research investigates the role of working memory (WM) capacity in sentence comprehension in three populations: young normal adults, normal elderly adults, and patients with probable Alzheimer's Disease (AD). The following questions are investigated: l) Do different aspects of sentence processing differ in the demands they place on WM? 2) Within a given sentence processing operation, does the demand on WM capacity increase as a function of increasing distance between crucial elements in the sentence? 3) Are impairments in sentence comprehension in AD and perhaps elderly populations secondary to limitations in working memory capacity or do they reflect deficits in the use of linguistic information? Both "sentence processing" and "working memory" are treated as cognitive systems with multiple subcomponents. This view is reflected in the experiments: Multiple measures of WM are collected from all three populations, and the sentence processing experiments are designed to isolate individual processes that contribute to language comprehension. After individual processes have been isolated, later experiments examine these processes in combination, e.g. how syntactic and semantic information combine to aid ambiguity resolution or pronominal reference selection. The sentence processing studies use an "on-line" cross-modal naming task. On-line methods are rare in elderly and AD research but are valuable because they measure the linguistic representation as it is being developed and can therefore pinpoint specific subprocesses of sentence comprehension. WM is investigated during sentence processing in three ways: l) through comparisons in sentence processing performance and WM capacity across the three populations and development of detailed profiles of individual patients' sentence processing abilities and WM capacity, 2) through comparisons across different sentence processing operations hypothesized to require different amounts of WM capacity, and 3) within a sentence processing operation through manipulation of the distance between two elements in the sentence that must be linked in the mental representation. The results will provide a detailed account of the role of working memory in sentence comprehension and will bear directly on theories of normal language performance and the impairments associated with aging and Alzheimers disease.